Astrocytes communicate with one another through propagated waves of Ca+2 .signaling both to coordinate their own activity and to interact with neurons. The mechanism responsible for the propagation of intercellular calcium waves between astrocytes involved two parallel pathways, one dependent on gap junctions and one that is gap junction-independent. For gap junction-mediated calcium wave propagation, diffusion of second messengers, such as 1P3, Ca2+, and/or cyclic ADP-ribose across cell boundaries is critical to sustain the regenerative event. By contrast, the gap junction-independent mechanism relies on the extracellular diffusion ofpurines and pyrimidmes released from one cell which then activates P2 receptors on the membranes of nearby cells. We have recently obtained evidence that astrocytes from Cx43 null mice display a different functional P2Y subtype expression compared to astrocytes from wildtype mice aTrd that this switch in purinoceptor subtype expression can markedly affect the extent to which calcium waves propagate through the extracellular space. These results thus lead to the overall hypothesis that purinoceptors and gap junction channels are functionally related, and that Cx43 regulates both modes by which astrocytes communicate with one another. It is possible that different selective permeabilities of gap junctions formed by different connexins or that remodeling of junctional complexes mediated through certain domains of connexins are involved in the interplay between connexins and P2Y receptors. To test these hypotheses we will up- and down-regulate expression levels of Cx43 and other gap junction proteins and measure changes in function and expression of P2Y receptor subtypes in the absence and presence of gap junction channel blockers. To evaluate whether the interplay between connexins and expression of P2Y receptors is mediated by specific domains of corinexins, we will express Cx43 lacking SH2/SH3 or PDZ sequences and test for changes in function and expression of P2Y receptor subtypes The consequences of such modification for cell-cell communication will be evaluated by measuring the properties of calcium wave spread and the strength of coupling. It is expected that by elucidating the interplay between gap junctions and P2 receptors in astrocytic intercellular communication, underlying mechanisms will be disclosed that dictate the extent to which long distance cell-to-cell signaling can propagate within the CNS.